A Hybrid-Assembly Strategical Draft Genome of Risso’s Dolphin, Grampus griseus

Duminda (University of Tokyo, Japan) explained how hundreds of animal genomes have so far been sequenced, and technologies for genome sequencing have progressed significantly over the past 50 years. Duminda described how the field of marine genomics has developed during this time, but despite the existence of over 200,000 known marine animal species, less than 500 of these animals have had their genomes assembled. Considering the number of marine animals at risk of extinction, genome sequencing may be important to aid their conservation.

Based on this awareness, Duminda aimed to sequence and assemble the genome of a Risso’s dolphin, which had been captured in a fishery. The Risso’s dolphin is permitted for use and trade as animal food locally and nationally, but not internationally. Duminda extracted genomic DNA and prepared two libraries for sequencing, one sequenced on a short-read platform, and the other on the Oxford Nanopore MinION device. With nanopore sequencing, scaffold-length reads were obtained and could be observed via real-time analysis. Hybrid assembly was performed using the LRScaf software. With the addition of MinION data, the read length N50 increased 7-fold and the BUSCO genome completeness score increased (from 57.1% to 78.2%); the final draft genome was 2.64 Gbp.

Duminda concluded that de novo genome assembly has been advanced with long-read sequencing technologies, and this may be the first long-read genome of Risso’s dolphin. He hopes that this resource will pave the way for other studies on gene/environment interactions, inbreeding, and local adaptations, to protect the future of this animal. His take home message: ‘Oxford Nanopore MinION is an easy and convenient tool for fisheries monitoring, stock assessment, and management’.